Blank images when used with WP Offload S3 (CDN)

When using WP Offload S3 (https://deliciousbrains.com/wp-offload-s3/), images and thumbnails are no longer generated and come up blank. When that plugin is disabled, the slideshow works fine. I did try and re-save the slide to make sure the cache is updated, etc. Any idea what's going on? Are the two not compatible?

HOWEVER, as I write this, everything works correctly if I leave "Main image width" and "Main image height" as well as "Thumb image width" and "Thumb image height" completely blank. So it has to do with those two settings?

Another question - the "Caption" option only puts the slide's title and not
description. How can I change this globally (using the WP plugin) so
there's the description HTML markup below the title? Any filters?